1. Field of the Invention
This invention relates to limit switches, and, more particularly, to a rotary lever operated limit switch having mechanism for increasing the degree of permissible overtravel during the course of a monitoring or sensing operation.
2. Description of the Prior Art
Rotary lever operated limit switches have been described in U.S. Pat. Nos. 3,252,345; 3,539,738; and 3,829,637 as having a head and a body portion fastened together. A shaft assembly is positioned within the head portion and an externally extending end thereof is attached to the lever. The body portion includes a switch, and the head portion includes a camming mechanism coupled to the shaft assembly to operate the switch in accordance with the rotary motion of the shaft assembly and the lever. After the shaft assembly has moved from its initial position to an actuating position in response to movement of the lever by a device being sensed, a mechanism is provided to return the shaft assembly to its initial position. This mechanism, which is described in the above referred to patents, is comprised of a spring loaded plunger which engages a flat cut away portion of the shaft assembly. In operation, as the shaft assembly is rotated from its initial position during a sensing operation, the plunger is forced to move upward into a recess within the head of the housing, and as the lever is released by the device, the plunger imparts a torque to the flat portion of the shaft assembly in a direction to return the shaft assembly to its initial position, whereupon a surface of the plunger presses against the flat portion of the shaft assembly. However, if the lever and shaft are moved approximately more than 60.degree. from its initial position, it is not always certain whether the plunger will be able to impart sufficient torque to the flat portion of the shaft assembly to return the shaft assembly to its initial position, since displacement of the shaft assembly beyond this 60.degree. position may cause the plunger to bear more against the circumference of the shaft assembly than against the flat portion of the shaft assembly. Thus, although the switch can be operated reliably within the range defined by the initial position and a 60.degree. angle of displacement of the shaft assembly, the overtravel which can be imparted to the lever and shaft assembly of the limit switch, while still enabling reliable operation of the switch, is thus undesirably limited. This limitation is undesirable, since the user of the limit switch is forced to be more precise in his installation of the switch in order to avoid damage to his equipment, if the switch is inadvertently or occassionally operated beyond this limit. Thus, in order to use this limit switch in many operations, great expense may be incurred by the user in order to precisely limit the maximum angular travel of the lever and shaft assembly of the limit switch.